hello

If i have letters with the following values assigned i.e a=1 b=2 c=3 d=4 e=5 etc,

then how can i get excel to return the results as follows: in cell a1 i put data say a,c,d to return the value 8 in cell a2, and if i then put in a,d,e, it then return the value 10 etc,i have tried vlookup but cant get it to work as all the data is all in one cell, help appreciated.